Exercise 4.9.5

Decrypt the message “NRQEUAPOM GLFN”, using the block cipher of Definition 4.121 and the key $1,1,1,2,2,2,3,3,3,4,4,4$. Hint: To decrypt, we must perform all the encryption steps in reverse. To undo a key mixing step, we subtract the relevant key components. To undo an S-box application, we apply the S-box in reverse. To undo a diffusion step, multiply by the inverse of the diffusion matrix.